1. Field of the Invention
The present invention relates generally to utility knives and more specifically to a spring loaded utility knife wherein the blade is constantly biased toward a retracted position so that upon the removal of manual pressure holding the blade in an exposed cutting position, the blade is automatically retracted to a non-exposed position under the bias of the spring.
2. Discussion of the Related Art
A number of utility knives have been proposed which have blade is arranged within a housing and arranged to project by an amount suitable for cutting paper, tape and the like. While these type of knives have found considerable utility, there has been a problem that the blade does not automatically retract upon the cutting operation being completed and requires that the operator take steps to have the blade move back within the housing of the device. One such device is disclosed in U.S. Pat. No. 5,813,121 issued on Sep. 29, 1998 in the name of Gringer. This device is such as to feature a side mounted slider which projects out of one side of the handle or housing and includes a series of positions in which the blade can be locked in a projected state. Due to the arrangement of the thumb piece being located on one side of the housing, this arrangement is limited to use by right handed people. Further, in the embodiments wherein a serpentine spring is used to retract the blade upon a lock mechanism is released, the spring, the blade carrier, the lock mechanism and the thumb piece are all integrally formed. The molding process required to achieve the production of this element is, of course, complex adding to the production cost. It further prevents the position/orientation of the blade carrier within the handle or housing from being varied to permit the use of differently shaped cutting blades and limits the degree to which the amount of projection of each blade can be adjusted in accordance with the task in hand.
U.S. Pat. No. 5,581,890 issued on Dec. 10, 1997 in the name of Schmidt, discloses a utility knife which permits the blade to be retracted back into the housing automatically upon the removal of manually applied pressure on a thumb piece. Nevertheless, this arrangement is provided with a rack on the interior of the housing and a projection on the blade carrier which is adapted to engage the rack in a kind of ratchet type of arrangement. This of course inhibits the change of the blade carrier orientation within the housing and thus prevents the use of a variety of different types of blades in the same device.
A further drawback that both of the above arrangements suffer from is the manner in which the two halves of the handles interconnect with one another. While the arrangement in U.S. Pat. No. 5,813,121 attempts to render the halves readily disengageable from one another via the provision of a latch member which is mounted on a flexible portion and arranged to bent via the application of a digit such as the operator""s thumb, the arrangement tends to be relative fragile and apt to fail after a large number of operations. The arrangement disclosed in U.S. Pat. No. 5,581,890, on the other hand, is such as to use a barbed member which snaps into a locking position once inserted sufficiently through an aperture formed in the other half. In this arrangement the ability to separate the two halves has not been given much consideration tends to be difficult to separate once they are engaged with one another.
Accordingly, there exists a need for a utility knife which is readily separable into its two halves, which has an engaging mechanism which is robust and which is not apt to fail after a relatively small number of operations, and which allows for a variety of different blades to be mounted and used in accordance with the desires of the user.
The present invention therefore is such as to feature a housing which has a unique engagement arrangement which is both robust and which allows with a simple press of the thumb, the two halves to be force apart to a state where disassembly of the knife is facilitated and quick and easy blade replacement/adjustment is rendered possible.
The present invention further features a blade carrier which is disposed in the housing and which can be, once the housing is popped open, adjusted with respect to an engaging portion formed on a thumb pieces to adjust the maximum amount of blade projection, or inverted so as to accommodate a different type of blade and allow for different cutting operations.
A further feature of the present invention is the ability to store spare blades within the housing, so that when the two halves are separated, switching from one type of blade to another is sped up in that the new and desired blade is immediately on hand and as such no searching about for the same is necessary.
Yet another feature of the present invention is the provision of a finger guard which is located on the lower edge of the housing. This guard allows the operator to place his or her index finger in a position wherein it is prevented from accidentally sliding forward toward the blade when projected.
In brief, the present invention is such that, in order to automatically retract the blade after cutting, a flat serpentine spring is integrally formed with a thumb piece which is slidably received in a slot formed along the upper edge of a housing/handle. The housing has a finger rest projection on the lower edge to facilitate cutting while the blade is projected with the thumb. The two halves of the housing snap together using a block-like projection formed on one half, and a pair of tabs formed on the other. The tabs, which are resilient, slide along the sides of the projection until recesses on each of the side of the projection are reached. Inwardly extending ridges on the ends of the tabs enter the recesses to provide a click lock. An aperture between the tabs allows pressure to be applied to the top of the projection to separate the two halves for blade reset/re-adjustment. The blade carrier, which is adapted to support two different types of blades, is slidably mounted in the housing so that it and the thumb piece are free of detents or click-locks. The carrier""s upper and lower edges have a number of apertures to permit setting in different orientations and adjustable positioning with respect to an engaging projection on the base of the thumb piece. This, in combination with the ability to set at least one of the blades in a plurality of different positions on the carrier, allows a high degree of blade projection adjustment.
More specifically, a first aspect of the present invention resides in a utility knife including a manually grippable housing comprised of first and second halves. The first and second halves cooperate to define an enclosed space therebetween and include connection means for permitting the first and second halves to be releasably connected to one another comprising: a) a shaped projection which is rigid with the first half; and b) a pair of resilient tabs formed on the second half, the pair of tabs extending along opposed sides of the projection to frictionally engage the opposed sides of the projection and hold the first and second halves together.
The above-mentioned connection means includes recessed portions formed in the sides of the projection in which ridge portions on the pair of tabs, are detachably received, and further comprises an aperture formed in the second half through which a top surface of the projection is exposed for manual manipulation and displacement of the projection away from the second half when disconnection of the first and second halves is required.
A blade carrier is disposed in the enclosed space and arranged to be slidable along elongate guide surfaces which project from at least one of the first and second halves. This blade carrier is adapted to receive two different blades and is disposable on the elongate guide surfaces in two distinct orientations. The blade carrier is adapted to support a cutting blade in a plurality of positions. In fact the blade, which is supported on the blade carrier, can be, in the instance its construction permits, set on the blade carrier in at least two different positions which determine the degree of projection of the blade from the housing when the blade carrier is manually urged to a blade extending position.
A thumb piece is slidably disposed in an elongate opening formed along an upper edge of the housing, and is detachably connectable with the blade carrier through a plurality of connection sites formed on one of the thumb piece and the blade carrier to allow the relative position of the blade carrier with respect to the thumb piece to be adjustable and for the degree of projection of a blade mounted on the blade carrier from the housing when thumb piece is moved to one end of the elongate opening, to be selectively varied. A spring is connected to one end of the thumb piece and is connectable at a second end to a portion of one of the first and second halves. In fact, in the preferred arrangement, the spring is unitarily connected with the thumb piece and has a flat serpentine configuration.
In one embodiment of the invention the serpentine spring has a plurality of inflexion portions at which the direction of the spring changes. Each of these inflexion portions has a dimension which is greater than the corresponding dimension of the portions of the spring which extend between and interconnect each of the inflexion portions.
In accordance with the preferred operation at least one of the thumb piece and the blade carrier are slidably supported by the housing so as to be smoothly slidable and free of engagement with detent or click lock structures and thus automatically and unimpedely biased to a blade retracting position under the influence of the spring when manual pressure on the thumb piece is absent. In addition to this the first and second halves of the housing are shaped to form a finger rest which is located on a lower edge of the housing so as to be approximately opposite the thumb piece when the thumb piece is maximally moved toward a front portion of the housing from which the blade projects. To render the housing more aesthetically appealing and to permit the type of blade to ascertained at a glance one of the first and second halves are made of a transparent material.
In accordance with a second aspect of the invention, a utility knife has a housing comprised of first and second halves which are detachably connectable to one another to form a housing. The halves are adapted to slidably support a blade carrier therein. This blade carrier is configured so that it can be rotated through 180xc2x0 from a first position wherein a first type of blade can be operatively set thereon, to a second position wherein a second type of blade which is different from the first, can be operatively set thereon.
A thumb piece which is slidably supported in the housing has a projection which engages in a selected one of a plurality of connection apertures are formed along opposed sides of the blade carrier in a manner which adjusts the relative position between the thumb piece and the blade carrier when the thumb piece is in drive connection with the blade carrier. A finger rest is located on a lower edge of the housing so as to be approximately opposite the thumb piece when the thumb piece is maximally moved toward a front portion of the housing from which the blade projects.
A flat serpentine spring has one end rigidly connected to the thumb piece and a second end detachably connected to a connection member on an interior surface of one of the first and second halves of the housing. This spring has a plurality of inflexion portions at the locations where the direction of the spring changes, the inflexion portions having at least one structural dimension which is greater than the corresponding dimension of the portions of the serpentine spring which extend between and interconnect the inflexion portions. Further, the spring is arranged to elongate in the longitudinal direction of the housing and is such that the at least one structural dimension is a width dimension taken at right angles to the direction in which the spring elongates.
One of the first and second halves is made of a transparent material so that the serpentine spring can be observed therethrough.
A third aspect of the invention resides in a utility knife having first and second halves which are detachably connected to one another to form a housing, and a blade carrier slidably disposed in the housing, comprising: a flat serpentine spring which is disposed in the housing, the serpentine spring having a plurality of inflexion portions at the locations where the direction of the spring changes, the inflexion portions having at least one structural dimension which is greater than the corresponding dimension of the. portions of the serpentine spring which extend between and interconnect the inflexion portions, the flat serpentine spring being separate from the blade carrier and connected thereto through an intermediate member. The intermediate member is a thumb piece which is slidably disposed along an upper minor edge of the housing, the thumb piece being unitarily connected to one end of the serpentine spring.
A further aspect of the invention resides in a blade carrier, which features a flat plate-like blade support member; upper and lower blade-retaining edge members which extend normally from the upper and lower edges of the blade support member, at least one of the upper and lower edges being adapted to engage and slide along a guide member; a plurality of engagement recesses formed in both of the- upper and lower edge members; first positioning projection adapted to engage in a notch formed in an upper edge of a first type of blade, the first positioning projection being contiguous with the upper edge members; and a second positioning projection adapted to engage an opening formed in a central portion of a second type of blade.
The first positioning projection is located between the positioning recesses formed in the upper edge member and a first end of the blade holder and the second positioning projection is located proximate to a second end of the blade holder and spaced from both the upper and lower edges of the blade support member. The first blade is a trapezoidally-shaped member in which the plurality of recesses are formed along an upper edge which is shorter than an opposite edge along which the cutting edge is formed, while the second blade is a rectangularly-shaped blade and wherein the opening in the central portion thereof is elongate in a direction essentially normal to a cutting edge.
Each of the plurality of engagement recesses formed in the upper and lower edge members are adapted to engage a projection formed on a manually operable member in a manner to establish a drive connection between the blade carrier and the manually operable member. In fact, the engagement recesses in the upper and lower edges can be so located with respect to one another that the blade carrier is rotatable through 180xc2x0 and disposable in a position wherein drive connection between the manually operable member and the blade carrier can be re-established.
A major surface of the carrier is imprinted with a plurality of blade icons which respectively indicate the location and orientation of a plurality of blades that can be disposed on the carrier, and the blade carrier is adapted for disposition in a housing so as to be smoothly and unimpedely slidable therein in a manner which is free of engagement with detent or click lock structures.